Touch sensitive devices allow a user to conveniently interface with electronic systems and displays by reducing or eliminating the need for mechanical buttons, keypads, keyboards, and pointing devices. For example, a user can carry out a complicated sequence of instructions by simply touching an on-display touch screen at a location identified by an icon.
There are several types of technologies for implementing a touch sensitive device including, for example, resistive, infrared, capacitive, surface acoustic wave, electromagnetic, near field imaging, etc. Capacitive touch sensing devices have been found to work well in a number of applications. In many touch sensitive devices, the input is sensed when a conductive object in the sensor is capacitively coupled to a conductive touch implement such as a user's finger. Generally, whenever two electrically conductive members come into proximity with one another without actually touching, a capacitance is formed therebetween. In the case of a capacitive touch sensitive device, as an object such as a finger approaches the touch sensing surface, a tiny capacitance forms between the object and the sensing points in close proximity to the object. By detecting changes in capacitance at each of the sensing points and noting the position of the sensing points, the sensing circuit can recognize multiple objects and determine the characteristics of the object as it is moved across the touch surface.
There are two known techniques used to capacitively measure touch. The first is to measure capacitance-to-ground, whereby a signal is applied to an electrode. A touch in proximity to the electrode causes signal current to flow from the electrode, through an object such as a finger, to electrical ground.
The second technique used to capacitively measure touch is through mutual capacitance. Mutual capacitance touch screens apply a signal to a driven electrode, which is capacitively coupled to a receiver electrode by an electric field. Signal coupling between the two electrodes is reduced by an object in proximity, which reduces the capacitive coupling.
Touch sensitive devices that capacitively measure touch are sometimes comprised of one or more electrode arrays extending across of transparent, touch sensitive surface. The number of electrodes that comprise such electrode arrays can be quite large, for example fifty or more such electrodes are possible. Further, for touch sensitive devices disposed in front of electronically addressable displays (such as liquid crystal or plasma displays), the number of electrodes in such electrode arrays is a function of the size of the display, and the number of electrodes that comprise an electrode array can grow to the hundreds. The individual electrodes are electrically connected to controller electronics with one or more flexible circuit tails having one conductor for each electrode in the electrode array, that is, an electrode array having 48 electrodes might have four tail connectors fastened thereto, each coupling twelve of the electrodes to controller electronics.